var a=1;
function add() {
	var x=document.getElementById("abc");
	if(a%2==0){
		x.innerHTML= "<button type=\"button\" class=\"btn btn-success\" onclick=\"add()\">123</button>"
		a+=1;
	}else{
	x.innerHTML= "<button type=\"button\" class=\"btn btn-success\" onclick=\"add()\">123</button>"+"<ul "+"class=\"nav nav-sidebar\">"+"<li><a href=\"\">"+"Nav item"+"</a></li>"+"<li><a href=\"\">Nav item again</a></li>"+"</ul>";
	a+=1;
	}
}